Balance impairment in general, and vestibulopathy (VSP) in particular, cause disability that accounts for substantial morbidity and decreased quality of life, particularly among older adults. The efficacy of vestibular rehabilitation programs for locomotor instability has to date not been investigated rigorously, although clinical evidence supports its use. Further, current biomechanical models of human instability are chiefly limited to standing "posturography" tests. Because all project patients will have postural instability, we apply sophisticated modeling techniques to better understand the biomechanical correlates of instability during standing, and activities of daily living (ADL) including gait, stair climbing and transferring from sitting to standing. The aims of the proposed investigation are to: (1) Determine the efficacy of vestibular rehabilitation (VR) for mid-life to the oldest-old VSP patients. We hypothesize that 1) VR improves dynamic stability during standing and locomotor ADL tasks significantly more than general conditioning exercises; 2) Dynamic stability improvement correlates directly (r>.7) with head stability improvement; 3) Standing posturography, dynamic locomotor ADL and clinical measures will be significantly correlated (r>.7); 4) Normal elders receiving VR improve their dynamic stability about 50% less than matched subjects with VSP; and 5) On 1 year followup, greater than or equal to 80% retention of the 12 week post-test dynamic stability will be observed. (2) To develop better biomechanical models of dynamic stability in older VSP patients. We hypothesize that 1) CG momentum and displacement characterize patients' stability significantly better than CP displacement alone, and 2) Whole body kinematic data can definitively characterize dynamic stability strategies. We propose to study 100 VSP patients in a randomized, double-blind prospective clinical trial of vestibular rehabilitation. Assessments at 0, 6 and 12 weeks will be conducted for all subjects. Half will receive VR starting immediately after intake, while another group will receive general conditioning exercises for 6 weeks. Following the 6 week re- test, the conditioning exercise group will receive specific vestibular rehabilitation. Fifty healthy, matched normals will receive VR between 0 and 6 week tests. At each test, quantitative vestibular function, posturography, full-body kinematic and kinetic analyses of ADL performance, and clinical data will be analyzed. In short, the methods used include sophisticated and expensive techniques and equipment that may not be available to most clinicians; we have, however, isolated these objective measurements from the rehabilitation process, the latter using "low technology" measurement and treatment approaches accessible in any clinic.